Thermionic valve system



Oct. 30, 1934. J ROBINSON 1,978,764-

THERMIONIG VALVE SYSTEM f Filed Sept. 26, 1950 2 Sheets- Sheet 1 Oct. 30, 1934. J. ROBINSON THERMIONIC VALVE SYSTEM Filed Sept. 26, 1930 2 Sheets-Sheet 2 Patented Oct. 30, 1934 PATENT OFFICE 1,978,764 THERMIONIC VALVE, SYSTEM James Robinson, London, England, assignor, by mesne assignments, to British Radiostat Corporation, Limited, a corporation of Canada Application September 26, 1930, Serial No. 484,671 In Great Britain October 8, 1929 v 6 Claims (Cl. 250--27) This invention is for improvements in or relating to thermionic valve systems, and is primarily concerned with such systems for the res ception and amplification of wireless signals.

Usually for efficiency it isadvantageous to em,- ploy circuits of very low damping or circuits having a provision for reaction adjustment to bring about an equivalent state, but there is the disadvantage that the system is unstable in that 1.0 self-oscillation may be set up e. g. initially by a signal of more than usual amplitude. An object of the invention is to provide an efi'icient system in which the possibility of self-oscillation being set up is obviated.

,15 The present invention comprises a valve systemin which self-oscillation is undesirable and which is unstable in operation or maybe ad.- justed (e. g. by means of reaction) to have such an unstable condition, comprising means to control the system to prevent self-oscillation, which means is rendered operative by, and according to the amplitude of, the energy in the system. 7

The invention also comprises a system as above wherein the controlling means aforesaid is ,a 5 valve or valves so arranged with regard to its electrical characteristics as to be inoperative when the amplitude of the energy in the system is below a predetermined value.

In one manner of carrying out the invention 7 the controlling valve is coupled to another valve in the system and in phase opposition thereto to give an output opposing'the energy in the system when it approaches the desired limit so as to balance out any increase above this limit. Further features of the invention will be apparent from the following descriptiontaken in connection with the accompanyingdrawings, in which l Figure 1 is a diagrammatic illustration of an electrical circuit employing the principles of the present invention; and

Figures 2 to 6 inclusive are similar diagrammatic illustrations each disclosing a modified form of the invention illustrated in Figure 1.

.45 Referring to Figure 1 of the drawings there is shown at 10 a valve which may be any of the high frequency amplifying or detecting valves of an amplifier or receiver for electromagnetic waves and is provided with means to give retroaction. The valve 10 is coupled at its input side to a tuning circuit comprising a coil 11 and variable condenser 12, the circuit being fed from an input coil 13. The output circuit of the valve includes a reaction coil 14, electromagnetically coupled to the coil 11, output terminals 15 and a direct current source indicated at 16. The valve 10 is in this case rectifying and the usual grid condenser 17 and leak resistance 18 are provided.

The coupling between the coils 11 and 14 is adjustable so that by tightening the coupling the retroaction can be increased to bring about a condition equivalent to very low damping which is desirable from the point of view of sensitivity and selectivity but has the disadvantage that the ad- 5 justment is critical and the system is liable to be set into self-oscillation by a signal of more than usual amplitude.

In order automatically to prevent self-oscillation means controlled by the signals is employed to provide an out-of-phase effect opposing any increase in energy in the system. In the example shown a controlling valve 19 is employed with its cathode connected to the cathode of the valve and 10 to a tapping on the coil 11. The grid of the valve 19 is connected through a condenser 20 to the coil 11 so that the signal energy is applied to this-valve in opposite phase to the energy applied to the detecting valve 10, and the output electrodes of the two valves are connected together so that the output circuit 14, 15, 16 is common to both valves.

The valve 19 is so biased negatively by means of a battery 21 in series with a resistance 22 that normally no signal effects reach the output circuit aforesaid. Should a signal of unusual amplitude be received exceeding the maximum for statable operation (e. g. by excessive adjustment of retro-action) an output is obtained from the valve 19 which, acting in opposition to the output of the normal valve 10, prevents the system from breaking into self-oscillation. The valve 19 may be so. selected as to have the required characteristics to enable the extra negative potential to be dispensed with.

Instead of employing a separate controlling valve there may be substituted for a valve of the amplifier or receiver, a valve with the appropriate electrodes to perform the normal function and also for controlling oscillation. In Figure 2 a valve 23 having two anodes, two grids and a single cathode has an input circuit comprising a coil 24 coupled to an input coil 42 and a condenser 25, connected in parallel between one grid and the cathode, a grid condenser 26 and leak resistance 27 being provided to give rectification. The anodes of the valve are connected by a reaction coil 28 variably coupled to the coil 24 and the output circuit is derived from a tapping on this coil 28 connected through output terminals 29 and a battery 30 to the cathode of the valve. The anode and grid to the left in the figure operate in the normal manner and the two girds are coupled through a battery 31 to give the grid at the right hand side a negative bias such that an output from the associated anode giving reversed reaction effects is only obtained when the signal energy exceeds a desired limit.

Figure 3 shows a modification of the system illustrated in Figure 2 and employing a valve having, instead of two grids coupled through a biasing battery, a single grid 39 that has a structure which is diiferent for the two anodes. As indicated the grid is ofcloser mesh at the part opposite one anode than it is at the part opposite the other anode.

Figure 4 illustrates another modification in which a single grid is used in valve 23 and this grid is of a high resistance wire through which a current is passed from the batteryBl to provide the required working potential variation for the grid.

The required differences in operation of the two parts of the valve 23 may be obtained by using different voltages for the anodes for example as shown in Figure 5. In this case the direct cur-'- rent supply from the battery 30 is fed through a choke-33 to one anode and an additional voltage is applied to the other anode by means of another battery 34 connected in series with a choke 35 between the two anodes. In a modification shown in Figure 6 the direct current supplies for the two anodes may be obtained independently from the battery 30 through chokes 36 and 3'7 respectively.

It will be understood that the invention is not limited to the several embodiments herein described but that any other suitable construction or circuit arrangement may be employed to obtain the desired automatic control of a thermionic valve system.

I claim:-

1. A thermionic valve system comprising the combination of a valve having in addition to a cathode and input and output electrodes connected respectively to input and output circuits, of an auxiliary output electrode in said valve connected to said output circuit in phase opposition to the first and means associated with one of the input and output electrodes for preventing an output from the auxiliary output electrode except when the output from the other output electrode exceeds a predetermined value,

whereby further increase of the energy in the system is prevented.

2. A thermionic valve system comprising the combination of a valve'having in addition to a cathode, a control electrode and an anode, an auxiliary anode, an output circuit to which said anodes are connected in phase opposition, said control electrode comprising a resistance element and means for passing an electric current through said resistance element to provide operating potentials at the control electrode to prevent an output from the auxiliary anode except when the output from the other anode exceeds a predetermined value whereby further increase in the energy in the system is prevented.

3. A thermionic valve system comprising a valve having input and output electrodes, electric circuits coupled to said electrodes, an additional output electrode in said valve connected to the,

output circuit in phase opposition to the first, said input electrode being constructed as a grid of closer spacing for that part adjacent one output electrode than for the part adjacent the other output electrode.

4. A thermionic valve system comprising the combination of a valve having in addition to a cathode, input and output electrodes connected respectively to input and output circuits, an auxiliary output electrode in said valve connected to said output circuit in phase opposition to the first, and means for producing a potential difference between the said output electrodes for preventing an output from the auxiliary output electrode except when the energy in the system exceeds a predetermined value.

5. Apparatus for preventing self-oscillation in a thermionic valve system characterized by low damping, comprising an input circuit, valve means associated with said circuit, said valve means including a main output electrode and an auxiliary output electrode, an output circuit associated with said output electrodes, means for connecting said valve means to said input and output circuits in such manner that the energy output of said electrodes is delivered to said output circuit in difierent phase relation, and means for blocking delivery of energy from said auxiliary output electrode when the amplitude of the energy in the said circuits is less than a predetermined value.

6. A radio receiving apparatus with high selectivity comprising the combination with at least one receiving valve, input and output circuits associated therewith, signal feeding means for said input circuit, and means retroactively coupling said input and output circuits in order to reduce the effective damping of the said circuits whereby the valve tends towards instability, of auxiliary thermionic valve control means connected to said input and output circuits in parallel with the said receiving valve and feeding signal energy from said input circuit to said output circuit in phase opposition to the said receiving valve, and means suppressing the output of the auxiliary thermionic valve control means when the amplitude of the energy developed in said circuits is below a predetermined value.

' JAMES ROBINSON. 

